Fire detection apparatus



Jan. 16, 1962 s. J. MESSELT 3,017,

FIRE DETECTION APPARATUS Filed Oct. 8, 1959 INVENTOR.

j STEPHEN J. MESSELT mm tatcs 3,0175% Patented Jan. 16, .1952

Free

ration of New York Filed Oct. 8, 1959, Ser. No. 845,280

1 Claim. (Cl. 250-83.3)

This invention relates to fire detection systems and, more particularly,to a portable, infra-red fire detection apparatus.

Many scientific advances have been made in the field of fire fighting inthe past few years. Many of these advances are at least partiallynullified, however, by the difficulty of pin-pointing the exact locationof hidden blazes. Smoke is one of the major problems of all firefighters. Smoke fills a building in a matter of moments, obscuring thefire. Not only can the blaze continue its destructive course behind theobscuring screen but extensive water damage may be done in the necessaryeffort to reach all possible points of combustion.

Furthermore, even the apparent extinguishment of a fire may not resultin its eradication. Unseen blazes often remain within walls andpartitions. There is little visible indication of the existence of suchfires. A fireman may use his hand to locate hot spots on a wall but thisis a slow and time consuming procedure. Fires within wall spaces arenotoriously rapid spreading. Air spaces act like flues in spreading theblaze from floor to floor.

It will be readily appreciated that firemen investigating burningbuildings, carrying protective equipment, working under all sorts ofweather conditions and in all types of structures, cannot be burdenedwith heavy, cumbersome equipment. This is particularly true when hasteis imperative.

It is, therefore, the primary object of the present invention to providea fire detection apparatus.

Other objects of this invention are to provide such an apparatussensitive to infra-red radiation; having a selfcontained power supply;portable and easy to handle by one man; fast acting and reliable; andrugged and adaptable to operation under severe conditions.

The above objects are achieved by providing fire detection apparatusincluding focusing means adapted to receive and focus radiation from aninspected area and a detector positioned at substantially the focalpoint of the focusing means. The detector is part of an electroniccircuit designed to produce an electrical signal responsive to theradiation. Indicating means are also provided responsive to theelectrical signal to disclose the presence of fire in an inspected area.

The manner in which the above objects are attained will be more apparentfrom the following description taken together with the figures of theattached drawing, wherein FIG. 1 is a sectional elevational view of adetection apparatus of the invention; and

FIG. 2 is a schematic block diagram of a circuit usable in the presentinvention.

The apparatus of FIG. 1 includes a tubular barrel member which may beconstructed of metal or other suitable material. A pistol grip 12 isprovided to afford the user a positive, comfortable grip. A window 14 isenclosed within the barrel near its open end. A paraboloidal mirror 16is positioned within the barrel to receive rays of entering infra-redradiation 18. Infra-red detector 20 is positioned on a bracket 22 at thefocal point of reflector 16. A toroidal supporting member 24 is securedwithin barrel 10 as a support for mirror 16 which is bonded thereto.Member 24 may be of any suitable material but in the illustratedembodiment is of rubber or plastic to provide shock absorbing qualities.The

necessary circuit elements are reduced to printed circuit form and arepositioned as members 26 within the barrel by means of supporting screws28. A meter 30 for visual observation is mounted at the rear of theapparatus, electrically connected to the circuit by wires 32. Wires 34are connected to a calibration knob 36. The wires interconnecting thedetector and the various printed circuit boards are not shown. A battery38 positioned within a suitable compartment within grip 12 provides thenecessary power for operation.

The electrical circuit of the device as illustrated in the block diagramof FIG. 2 includes the detector 20, preamplifier 40, amplifier 42,rectifier 44, and meter 30. A

variable oscillator 46 may also be provided along with head phones 48for producing an useful when visibility is limited. components is ofstandard construction and well known in the art, it has not beenconsidered necessary to illustrate the circuits in more detailedfashion.

The primary function of window 14 is to maintain cleanliness withinbarrel 10 and thereby protect the surface of reflector 16. Window 14,however, may also be used as a filter, for example, to eliminate visiblelight which might give erroneous readings.

For the detection of fire sources, a detector responsive to atemperature of approximately 210 F. is required. However, in order toprovide some margin of safety and, at the same time, compensate for theinsulating qualities of walls and partitions, the apparatus ispreferably made sensitive to heat sources of F. In addition, for maximumefficiency, the heat source should be detectable at a distance of tenfeet. The energy emitted by a black body radiator at 150 F. is 7X10watts/cm. By using a three inch paraboloidal reflector to focus theradiation, the available energy at a detector is approximately 1.26 10-watts.

The detector should be of the uncooled type and have a spectral responsewithin a wavelength band not absorbed by the atmosphere. Examples ofusable wavelengths are 3.5 to 4.3 and 5.0,!L. The noise equivalent powerof the detector should provide a good signal to noise ratio at 126x10watts.

Several detectors will satisfy the foregoing requirements-a bolometer,lead selenide, or lead sulfide, to name a few.

Because of the drift problems encountered in the DC. amplification ofdetector signals, it is preferable to utilize an AC. amplifier. In orderto do this, the signal must be chopped. In order to eliminate thenecessity for a mechanical chopper, the detector may be wired into anAC. bridge circuit excited by an oscillator. Any of a number of easilyportable battery sources may be utilized for a power supply. In thedescribed embodiment, a rechargeable 9 volt mercury battery is employed.

It will now be seen that in order to locate the existence of hot spots,an operator need only scan an area, such as a wall, by pointing theapparatus in the proper direction. The infra-red energy, guided throughbarrel 10 and focused on the detector by the reflector, will cause asignal to flow in the electrical circuit. The signal, amplified andimpressed on a meter or headphone, will thus give a physical indicationof the presence of fire.

It will be apparent that the device of the present invention has wideapplication in all fields in which the location of heat sources is ofimportance. It will be further apparent to those skilled in the art thatthe apparatus of this invention is capable of many variations. Thetubular radiation path, for example. is not limited to a construction ofcircular cross section but may be of any convenient shape such assquare, octagonal, or oval. The

foregoing description is therefore to be construed as descriptive ratherthan limiting.

audible signal especially As each of the electrical I claim:

Fire detection apparatus comprising a tubular barrel having an infraredpermeable window at one end thereof, said window being of substantiallydisk-like configuration and lying in a plane perpendicular to thelongitudinal axis of said barrel; pistol grip means attached to saidbarrel for supporting the apparatus in a users hand; paraboloidalreflector means positioned in said barrel to receive the radiationpassed by said window and focus said radiation on a finite area betweensaid window and said reflector; detector means selected from the groupconsisting of lead selenide, lead sulphide, and bolometers positioned toreceive the focused radiation, said detector being responsive toradiation Wavelengths selected from the group consisting of about 3.5;1,to 4.3 4 and approximately 5,u.; electronic alternating current circuitmeans within said barrel means for producing an electrical signalresponsive to the radiation on said detector; battery means within saidpistol grip for supplying electric power to said circuit means; andindicating means responsive to said electric signal to disclose thepresence of fire in an inspected area.

References Cited in the file of this patent Osborne: Airborne InfraredUNITED STATES PATENTS OTHER REFERENCES Warning System Measures Range,Electronics, July 1, 1957, pp. 190192.

Osborne: Infrared Detector Aids Medical Diagnosis, Electronics, October1, 1957, pp. 115-157.

